Monitoring in anaesthesia is important to assess the patient's physiological status and response to interventions. Basic monitoring includes clinical assessments while advanced monitoring uses instruments. Instrumental monitoring can assess the cardiovascular, respiratory, temperature, central nervous, and neuromuscular systems. Electrocardiography, blood pressure monitoring, capnography, pulse oximetry, and central nervous system monitors like the bispectral index and entropy are commonly used advanced monitoring methods. Each method has advantages and limitations that should be considered during anaesthesia.

1. MONITORING IN ANAESTHESIA

2. Why monitor anaesthesized pts?
• Anaesthetic agents – Cardiopulmonary depressants
• Patient’s response to interventions
• Proper functioning of anaesthetic equipment
Monitoring can be divided into
• Basic:
Basic Monitoring includes clinical monitoring. Ex: Pulse rate, Blood pressure, inflation of chest,
color of skin.
• Advanced:
Advanced Monitoring includes instrumental monitoring.

3. Advanced Monitoring
Instrumental monitoring for different systems in our body with some examples are as
follows:
• Cardiovascular system monitoring:
• Non-invasive Ex: ECG, Non-invasive blood pressure ( NIBP )
• Invasive Ex: Invasive blood pressure (IBP), Central venous pressure(CVP)
• Respiratory system monitoring : a) Pulse oximetry b) Capnography
• Temperature monitoring
• Central nervous system monitoring Ex: a) Entropy b) BIS
• Neuromuscular monitoring Ex: TOF monitor
• Some commonly used monitoring methods are discussed below.

4. • Electrocardiography is the procedure of recording the electrical activity of the
heart.
• The electrode combination records the difference of potential between two sites
on the body. The potential differences are produced due to the electrical activity of
the heart.
• The three primary reasons for ECG monitoring are continuous monitoring of heart
rate, identification of arrhythmias and conduction abnormalities, and detection of
myocardial ischemia.

5. Electrocardiogram Lead Placement And Selection
• Standard Lead Systems:
• Current operating room and intensive care monitoring systems have five leads that allow
monitoring of the standard limb leads (I, II, III), the augmented limb leads (aVR, aVL, aVF),
and a single precordial lead (V1, V2, V3, V4, V5, or V6).
• Typically, two of these 12 standard leads are simultaneously displayed on the bedside
monitor.
• Based on AHA guidelines, ECG monitoring leads have a standard color-coding system: right
arm (white), left arm (black), right leg (green), left leg (red), and precordial lead (brown)

7. Parts of ECG
• Electrocardiograph is the
machine
• Electrocardiogram is the
record
• The characteristic shape and
timing of the ECG waves are
due to the spread of wave of
depolarization and
repolarization associated with
each heartbeat.

8. Parts of ECG

9. ECG Monitoring for Myocardial Ischemia
● The ST segment is the ECG component most sensitive to acute myocardial ischemia.
● ST elevation indicates transmural ischemia and is most often the result of acute coronary
artery occlusion
● Ischemia confined to the Subendocardial area is usually denoted by ST-segment
depression.
● Subendocardial, ST-depression–type ischemia typically occurs during episodes of
symptomatic or asymptomatic (silent) stable angina pectoris, and is characteristic of
ischemia occurring during exercise, tachycardia, or pharmacologic stress testing in
patients with significant but stable coronary artery disease.

10. BLOOD PRESSURE MONITORING
A. Indirect Measurement Of Arterial Blood Pressure:
Manual Intermittent techniques:
● The systolic pressure was identified using an inflatable elastic cuff around the arm
and a mercury manometer to measure cuff pressure, while the radial arterial pulse
was palpated as the cuff pressure was increased or rapidly decreased.
● The technique was later modified to detect both systolic and diastolic pressure with
description of auscultatory method of blood pressure measurement by Korotkoff .
● Korotkoff sounds are a complex series of audible frequencies produced by turbulent
flow beyond the partially occluding cuff.
● The systolic pressure is associated with first sound heard (beginning of turbulent
flow through the vessel) and diastolic pressure at the point when the sounds
disappear (when vessel flow becomes laminar).

11. Blood Pressure Monitoring
● Mean blood pressure cannot be measured using this technique.
● A fundamental principle of the auscultatory method is its reliance on blood flow to
generate Korotkoff sounds.
● Physiologic conditions that interfere with sound detection (e.g., severe edema,
obesity, abnormal compliance of overlying tissue) or blood flow (shock, intense
vasoconstriction) will frustrate manual blood pressure measurement.
● Furthermore, the cuff must also be snugly fitted, with a bladder that measures 40%
of arm circumference and 80% of length of the upper arm, and centered over the
artery.
• Small cuff for children
• Cuff too large – underestimates BP
• Cuff too small – Overestimates

12. Automated Intermittent Techniques:
● Automated noninvasive blood pressure (NIBP) devices are the most commonly used
means of measuring blood pressure in the operating room.
● Small oscillations in pressure amplitude are measured in an air-filled cuff that slowly
deflates from a pressure well in excess of that needed to collapse the underlying artery.
● The point of maximal oscillation marks the mean arterial blood pressure (MAP), with
systolic and diastolic being calculated by various proprietary algorithms specific to
individual device manufacturers.
Complications of Noninvasive Blood Pressure (NIBP) Measurement:
● Pain
● Petechiae and ecchymoses
● Limb edema
● Venous stasis and thrombophlebitis
● Peripheral neuropathy
● Compartment syndrome

13. B. Direct Measurement Of Arterial Blood Pressure:
Indications for Arterial Cannulation:
● Continuous, real-time blood pressure monitoring
● Anticipated pharmacologic or mechanical cardiovascular manipulation
● Repeated blood sampling
● Failure of indirect arterial blood pressure measurement
● Supplementary diagnostic information from the arterial waveform

14. Percutaneus Radial Artery Cannulation
● The radial artery is the most common site for
invasive blood pressure monitoring because it is
technically easy to cannulate and complications
are rare.
● Allen’s Test: The radial and ulnar arteries are both
compressed while the patient makes a tight fist to
exsanguinate the palm and then slowly reopens it.
As occlusion of the ulnar artery is released, the
color of the open palm is observed.
● Normally, the color will return to the palm within
5-15seconds. This is POSITIVE Allens test. If colour
does not return in 5 – 15 seconds implies
compromised collateral flow. Negative Allens test,
should not cannulate radial artery

15. Complications of Direct Arterial Pressure
Monitoring
● Distal ischemia
● Pseudoaneurysm
● Arteriovenous fistula
● Hemorrhage
● Arterial embolization
● Infection
● Peripheral neuropathy

16. Mechanism of IBP Monitoring
Principle: Strain gauge principle,
Wheatstone Bridge circuit

17. Transducer Setup: Zeroing and Leveling
● Prior to use, pressure transducers must be zeroed, calibrated, and leveled to the appropriate
position.
● Zeroing establishes the zero reference point as ambient atmospheric pressure, while leveling
aligns this reference point relative to the patient’s body, determining where the value “0” will
be.
● Arterial pressure transducers should be placed to best estimate aortic root pressure. The best
position for this is approximately 5 cm posterior to the sternal border which corresponds to
halfway between the anterior sternum and the bed surface in the supine patient.
● During a sitting neurosurgical procedure, it may be more informative to place it at the level of
the patient’s ear to approximate the level of the Circle of Willis.

19. Normal Arterial Pressure Waveforms:
● The systolic waveform immediately follows the ECG R
wave and consists of a steep pressure upstroke, peak,
and ensuing decline.
● The downslope of the arterial pressure waveform is
interrupted by the dicrotic notch, continues its decline
during diastole after the ECG T wave, and reaches its
nadir at end-diastole.
● The dicrotic notch of a central aortic pressure
waveform is sharply defined and thought to result
from aortic valve closure.

20. Central Venous Pressure Monitoring
● .

21. Common sites of CV Cannulation

23. CVP Wave

25. CAPNOGRAPHY
• Capnography is the continuous, noninvasive measurement and graphical display of end-
tidal carbon dioxide (ET C02 ) concentration versus time (Time Capnogram) or expired
volume (Volume Capnogram) during a respiratory cycle.
• Capnograph is the machine that generates a waveform
• Capnogram is the actual waveform.
• Capnometry is the measurement and numerical display of maximum inspiratory and
expiratory C02 concentrations during a respiratory cycle.
• Capnometer is the device that performs the measurement and displays the reading.
• ET C02 is the partial pressure of carbon dioxide (C02 ) at the end of an exhaled breath,
which is expressed as a percentage of C02 or mmHg.
• The normal values are 5% to 6% C02 , which is equivalent to 35-45 mmHg.

26. Physics of CO2 Measurement
• Methods to measure C02 levels include
• Infrared spectrography
• Mass spectrography
• Raman spectrography
• Photoacoustic spectrography
• Chemical colorimetric analysis.

27. Infrared method
• The infrared method is most widely used.
• C02 strongly absorbs infrared light with a wavelength of 4280 mcm.
• So infrared light is emitted from a hotwire and filtered to obtain the desired wavelength.
• This infrared radiation passes through the sample chamber where it is absorbed by C02
and the remaining unabsorbed radiation is focused onto a detector with a semiconductor
that creates an electrical signal.
• The concentration of C02 is directly proportional to the amount of infrared light absorbed;
and the higher the C02 concentration in the gas mixture the more infrared radiation is
absorbed and less arrives to the detector.
• This method allows for real time, continuous measurement, and display of PC02 with a
delay time of approximately 0.25 seconds. Nitrous oxide, which absorbs infrared light at a
relatively close wavelength, may interfere with the measurement of C02 concentration.

29. Types of Capnographs
The gas to be analyzed reaches the sample
chamber in 1 of 2 ways :
• A mainstream analyzer that resides
within the breathing circuit, usually
between the end of the endotracheal
tube and the Y connection.
• The second method is side stream
analyzer, in which the gas sample is
aspirated from the breathing circuit
through a 6-foot-long small capillary
tube to a remote analyzer. The rate of
gas sampling can usually be adjusted
from 50 to 500 ml/min. .

30. Mainstream Analyser
Advantages:
• Sensor at patient airway
• Fast response
• Waveform
• Short lag time (real time )
• No sample to reduce tidal volume
Disadvantages:
• Secretions & humidity block sensor
• Sensor heated to prevent condensation
• Bulky sensor at patient airway
• Does not measure N20 patient
• Difficult to use in unintubated
• Contamination of sensor

31. Sidestream Analyser
Advantages:
• No bulky sensor / heater at airway
• Ability to measure N20
• Disposable sample line
• Can be used in unintubated patient
Disadvantages:
• Secretions block sample tubing
• Water trap required
• Slow response to C02 changes
• Sample flow reduces tidal volume

32. Factors influencing accuracy of EtCo2
Monitoring
• Presence of nitrous oxide (N20) and oxygen(02 ) They both artificially increase the
C02 measurement because they absorb IR light at a similar wavelength as C02.
• Atmospheric pressure In the event of change in atmospheric pressure, their
conversions are altered accordingly. Every 20 mmHg change in barometric
pressure will create a 1 mmHg C02 measurement error, if uncorrected.
• PEEP Application of PEEP increases the C02 reading. A PEEP of 20 cm H20
increases the C02 reading by 1.5 mmHg.
• Influence of water vapour: The presence of water vapour condensation in
sidestream, results in an overestimate of PC02 , since, water that has a high IR
absorbance enters the cell. An effective water separation system is required for
continuous use. A water trap is used in sidestream analysers to remove water in
particulate form.

33. Types of Capnograms
Two types of capnograms:
• Time Capnogram
A typical time capnogram can be considered as two segments, an inspiratory
segment and an expiratory segment and two angles, an alpha and a beta angle.The
capnograph is divided into four distinct phases: Phase I, II, III &0.
• Volume Capnogram

37. Pulse Oximetry

38. Physics Of Pulse Oximetry
Physics:
• Detection of oxygen saturation of haemoglobin by pulse oximetry is by
spectrophotometry and optical plethysmography (which measures pulsatile changes
in arterial blood volume at the sensor site).
• It is based on Beer - Lambert law, which states that if a known intensity of light
illuminates a chamber of known dimensions, the concentration of the dissolved
substance can be determined if the incident and transmitted light intensity is
measured

39. Basic Design Of Pulse Oximeter
• It has 2 LED and a photodetector sensor.
• One LED emits light at 660 nanometer(red) and other at 940nm(infrared).
• Oxygenated hemoglobin absorbs more infrared light and allows more red light to
pass through.
• Deoxygenated haemoglobin allows more infrared light to pass through and
absorbs more red light.
• The photodetector sensor measures the amount of red light and infrared light
that pass through.
• The ratio of the red light measurement to the infrared light measurement is then
calculated by the processor ( which represents the ratio of oxygenated
hemoglobin to deoxygenated hemoglobin).
• This ratio is then converted to Spo2 by the microprocessor via a lookup table
based on the BEER- LAMBERT law.

40. Parts of Pulse oximeter probe

41. Types of Pulse Oximetry
Two types of pulse oximetry:
• Transmissive application mode
• Reflectance pulse oximetry
Transmisive is the common type. Sensor device
is placed on thin part of patient’s body, usually
a fingertip or earlobe or in case of infant ,
across the foot

42. Indications

43. Limitations

44. CNS MONITORING
Objective Methods Of Depth Of Anaesthesia Monitoring:
Electroencephalogram and Derived Indices
In 1937, Gibbs et al reported that anaesthetics changed EEG activity from low-voltage fast
waves to high-voltage slow waves and postulated that the EEG could be used to measure
the effect of anaesthesia.
The EEG is a continuous, responsive, noninvasive indicator of cerebral function even when
the patient is unconscious and unresponsive.
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2023
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46. Bispectral Index
• BIS empirically derived scale
proposed by aspect medical systems
in 1994.
• The algorithm processses the EEG
and gives a index value between 0 to
100.
• It is based on 3 EEG analyses:
spectrogram, bispectrum and time
domain assessment of burst
suppression.

48. Advantages and Disadvantages
Advantages
• Changes in index are correlate with level of consicousness, used for prevention of
intraoperative awareness.
Disadvantages
• BIS is a cortical function indicator, not subcortical structures(spinal cord) that
mediate motor response to a noxious stimulus.
• Thus, BIS may not be reliable for predicting responsiveness to noxious stimuli.
• Electromechanical interferace with pacemakers/electrocautery cause artifacts –
increase BIS value
• Reduced CMR – cardiac arrest/hypotension/hypoglycemia/hypothermia/cereberal
ischemia- low BIS
• Epilepsy or cerebral palsy- change BIS depending on associated EEG changes.
• The presence of senile dementia may be a confounding factor in interpretation of
BIS value.
• BIS response is less reliable with a high dose opioid technique.

49. Entropy
• It was commercially developed by Datex – Ohmeda.
• Entropy is a quantitative EEG device that uses a complex algorithm to generate two
numbers that are derived from different frequency bands.
• The State Entropy (SE) is calculated from the 0.8Hz to 32Hz range, whereas the Response
Entropy (RE) uses frequencies upto 47hz.
• Electromyogram activity is more predominant in those higher frequencies, and so the
Response Entropy may respond more quickly when muscle activity is present.

50. Entropy Values

51. Entropy advantages
• reliable as BIS.
• validated for propofol, thiopental, sevoflurane and desflurane anaesthesia.
• Less interfered with the electrocautery unit than BIS during intraoperative period.
Entropy disadvantages
• entropy is unreliable during high dose opioid anaesthesia.
• Paradoxically high readings for ketamine and nitrous oxide.
• Low entropy value with dexmedetomidine doesnot indicate profound state of
unconsciousness